Apparatus for gas plating continuous length of metal strip



APPARATUS FOR GAS PLATING CONTINUOUS LENGTH OF METAL STRIP Filed June24, 1954 May 26, 1959 F. E.'-DRUMMOND 2 Sheets-Sheet 1 INVENTOR FOLSOM5. ORUMMOND VACUUM PUMP ATTORNEYS May 26, 1959 F. E. DRUMMOND APPARATUSFOR GAS PLATING CONTINUOUS LENGTH OF METAL STRIP 2 Shgets-Sheet 2 FiledJune 24. 1954 VACUUM PUMP United States Patentc) APPARATUSYFOR. GASPLATINGCONTINUQUS LENGTH OF'METALSTRIP Folsom-E; 'Drummond, Washington;'D.C.,'-' assignor to The Commonwealth Engineering Company of Ohio,Dayton, Ohio, a corporation of Ohio Application June 24, 1954,Serial'No. 439.975 If;

1 Claimw c1. 11s-4s This invention; relates to the art of gaseousdeposition of metals. The invention more particularly is concerned Iwith the preparation of gaseous plated'metal products and improvedprocesses for carrying osition.

out gaseous metal depln the preparation of coatings-as obtained for exam'le -by gaseous metal deposition-of metal'carbonyls, it-has beenproposedto produce-such metal coatings by treat-' ing the base metal, in theform of a strip or other article,

-which has been mechanically or chemically -'clea ned,- to gaseous-metaldeposition by heating'the material in an atmosphere containing theheatdecomposable gaseous metal compound and thereafter subjectingthegaseous metal treated article to heating-to produce -a relativelysmooth, uniform; coherent continuous metal coating. The

present invention distinguishes from the priorprocesses in that themetalbase ormaterial to be plated "is sub jected to a pre-treatment toproduce adry, 'deaer-ated metal surface for receiving the-gaseous metalcoating.

The invention thus makes it possible for the first time "to produce ametal coating which is interlocked withthe base metal in such a manneras to produce a substantially integral product. The product thusdistinguishes from so-called wet-plating of metal surfaces, e.g;,aS-inelectrosurface. -Heretofore it has-been knownthat such pores andsub-microscopic depressions of the-surface" metal a could notbe platedutilizingthe so-calledwet processes,

wherein solutions containing the l'saltslxof the metal to be plated areutilized with,orswithout electrical means.

By the present invention a. product; is produced wherein the metal plateiscarried out utilizinglgaseou's heat/decomposable metals andlwherebythe metal to be .platedris initially heated todrive off all occludedgases: and While thus heated is subjected tozvacuum-or. reduced pressure.conditions. so as .to expunge the metal surface to be plated of allgases and permit the gases containing'the'gaseous metal to enter thepores and sub-microscopic.depressions .in the metal surface,andzdepositthe metal therein to .thus

forman interlocked substantially integral metal product.-

It vis the principal object ,of the: present invention-to produce agaseous metal coated product wherein the metal product produced is madeup .of a metal base and .a

\ coating which is substantially integral therewith.

Another object of the invention is toprovide an.;im-- proved method ofplating, utilizing gaseous :metal com= pounds and wherein the gaseousmetal deposition is-carthe base metal than has heretofore beeneffected-by-wet and dry methods of plating.

:It I is another object of the invention to -provide an improvedmethodof producing metal coatings whichcan withstand elevated temperaturesandbending stresses' with- {887,984 a n ed Me? to 195 ice out @causingblistering or peeling-"oftliefmetal coating.

' It is a further object-of the invention to"provided 1 method ofproducing metal coat'ed articles rhavin' a' co- 5 1 here'ntinterlockedmetal -surface*coating o'ver the metal "It is a still further object ofthe invention to provide a' product comprising a base metal'-"material"" which "is coated with uniformly deposited metal wherei'nthe'i'net'al coating is made to penetrate deeply-into='theihaselnetal I-and diffuse therein so as to become substantially integral withthe'base metal. p F

Theseand other objects arid'advdntages'tvill become apparent as thedescription proceeds, and taknin conjunction with thef'drawing'sformingapart of this specification, wherein:

Figure 1 illustrates diagr'arnr'naticallyandpictorially an 1 apparatusfor carrying out 'the' gaseous 'me'tal' 'platingfin =.a'c ordance withthis invention;

i Figure 2 is a'verticalcrosssectional View taken substantially on theIine"2+2 of Fi'gure'zl and" lookingfin thedi'rection ofthe arrows; r

Figure 3 is a similar cross-sectionalviewms inFigure ---2, takensubstantially on the line 3 3 banium: l, and

l'ookingin the direction of the arrows; v Figure '4 is a cross-sectionalview through the gaseous --"rnetal' plating chamber, taken"substantiallyF on tlie line arrows; Y Figure '5 is an 'enlargedfviewshowing 'a -nretal-article plated by the wet plating method;

Figure '6 is a similar View illustrating '-a like "cross-sectionof ametal strip plated in accoi'dance"with this in- -vention; w Figure-7 isa similar'viewin perspectiveas in Figure 1, illustrating amodificationof the apparatus and process therein,'and wherein the metal striptobecoated' is heated by means ofaclosed coil and the'deaeratibnchamheris substantially integral with the'gaseous deposition chamber,'providingamore-compact apparatns;'

I Figure 8 is a cross sectionalview' taken on-tl1e line 1 8-'-8 ofFigure-1', and'slooking in the dirction of the -arrows; V 3 Figure v.9is' a. somewhat eiilarg'ed -cross sectional view taken on the line '9'-9of Figure? l'g and" lookingin the direction of the arrows; 1 r a iFigure" 10 'is a similar sectional iview'take n substantially on theline10- 10 of Figure 9; and Io'Qking -in-the; direcition of'tthe-arrows; and

Figure 11 is a similar sectional view on a somewhatcnboularged scaletaken onthe'linei 11+1r'or Figuredfand looking in the direction ofthearrowsi i l In the preferred process 'ofithe inventionfand whichewwill be described with particular re'ferenceito the plating :of'a.continuous length metal strip-,uit'is undrstoo d that ::the'invention isnot to be restricte'dto th 'shapeorsize of the base metal to be plated.For examplwthe gaseous continuous process. In the embodiment shown. inFigures 1%:4 ofthdraw- 60. ingsya metal strip 10, which. maycomprise:steel;aluminum, copper, etc.,' and whichhas been-previously'cleaned vas by electro.chemical.or'isand't'blasting':ortthe like, ispassed over the roll 12 and thencefintothe cleaning bath .14,being drawnunder. the. spaced rolls :15 arranged in the :1 bottom of the cleaningtank 16. 3

l The cleaning bath 14 may comprise 'rinsewaten'or'ganic volatilesolvent, :e.'g., ethyl: acetate, acetone; petroleum solvent,-or mixturesthereofg'towashtliestripi-and remove anycgreaseand-foreign particles or's'pre cleaning' solution. 70. As the metal strip 10 is drawn upwardlyand over the roll18'itis subjected to an air. blast z-2'2.:w-hi'chpreferably comprises hot air as supplied from: the blower- 24iltliemetal ,platingimay. be carrieduout" as a continuous. ordisairbeingidrawn into the is drawn upwardly and over the roll 18 and thenceinto theheating chamber 20, the strip being moved along andcentrallybetween the vertically spaced electrical heating elements,- or.resistance coils 30. The heating elements 30 are connected to a sourceof electrical current by.

suitable conductors 32. The heating chamber 20 comprises an elongatedcompartment having insulated inner walls34 and a slot opening 36 for theentrance of the metalstrip 10, and a similar exit opening 37 at theopposite end, the heating chamber being suitably fabricatedfrom twohalves which are bolted together, as at 38 as shown in Figures 1 and 2.

. Joined to and communicating with the exit opening v37 of the heatingchamber 20 is a gas lock gate means 40 which comprises an I-shapedmember having a longi-.

tudinal slot opening 42 therethrough which is adapted to register withthe exit opening 37 so as to accommodate the passage of the metal strip10. Communicating with the opening .42 of the gas lock 40 are tubularconduits vide the gaseous gate interlocked between chamber 20 and thedeaerating chamber 47.

The deaerating chamber 47, as shown, preferably comprises an elongatedcylindrical chamber which is fitted 1 44 and 45-. throughwhich is passedthe inert gas to pro- 1 chamber 86 which is constructed and operatedsimilarly as the heating chamber 20. The finished plated strip'is drawnfrom the heat treatment chamber 86, and after cooling in the air, iswound up on the storage roll 88, as illustrated in Figure 1.

In a modification shown in Figures 7-11, the metal strip being treated,as shown at 10, is passed through a heating chamber 92, which chamberinthis instance is heated by the helical coils 94' through which heatedfluid, such as steam, hot water or the like fluid, is passed. Strip 10is supported and drawn centrally of the coils 94 so as to be evenlyheated. Conduits 96, 97 are connected to the chamber 92 and the coil 94for passing heated fluid through the coil.

After the strip 10 has passed through the pre-heating chamber 94 it isconducted into the vacuum or low pressure chamber 99 and thence into thegas plating chamber 100, and finally through the post heatingorannealing chamber 102, after which the finished gas plated metal strip10 is rolled up on the storage roll 104.

. The low pressure chamber 99 is provided with a pressure gauge 106, andthe conduit 108 which is in communication with the interior of thechamber is provided,

the conduit being connected to a vacuum pump or evaouatingprime moverwhereby the chamber 99 is kept under reduced pressure. Provision is madeat the inlet and exit of the strip for properly sealing the openings.

with apressure gauge 48 and conduits 50 and 52 for ,the admission andwithdrawal of gas from within the chamber147. ,Arranged within thechamber 47 are cooperating pairs of guide rolls 54 and 56 which arearranged to guide and support the metal strip 10 as the As ilsame isdrawn therealong through the chamber.

lustrated, the conduit 50 is open at its inner end 57 and communicateswith the chamber 47 the conduit being connected to a vacuum pump or thelike to provide a vacuum or reduced pressure chamber for drawing off anyoccluded as nitrogen, helium, carbon dioxide, etc., where it is desiredto introduce the same while subjecting the strip to reduced pressureconditions. In this manner a gaseous washing effect may be producedsimultaneously with the low pressure conditions as effected by thevacuum pump.

valve 58 is provided in the line .52 so that the same may gasesfrom thesurface of the metal strip before subjecting the same to gaseous metalplating. The conduit 52 is .prOVided for introducing inert gas orwashing gases, such be sealed 011 where it is desired to use only thevacuum for low pressure treatment in chamber 47.

v From'the deaerating chamber 47 strip 10 passes through gthfigdSfiOllSgate interlock 60 which is of similar construction and operation as gaslock gaseous gate interlock 40. i

' Thestrip isithus passed from thechamber 47 into the .the introductionthe the heat decomposable gaseous metal plating compound. At theopposite end a conduit 70 is provided. The gaseous metal compound ispreferably introduced through the conduit'69 and after circulatingthrough the chamber and in contact with the metal strip is withdrawn.through the exit conduit 70.

To assist in the even distribution and circulation of the gaseous metalcompound in the chamber 65, the

same is provided with helical-shaped baflies 74 and .76.

. An important aspect of applicants invention is the I municates withthe plating chamber at one end permits In this instance the gates 110,and 111 comprise sponge rubber seals which function as a squeegee toseal the strip as the same moves into and out of the chamber 99.Appropriate guide rolls 113 are arranged on the standard 114 and whichsupport and guide the strip 10 through the -low,pressure chamber.

1 In the gaseous plating chamber conduits 116, 118 are provided throughwhich the heat decomposable gaseous metal compound is introduced anddischarged respectively, as shown more clearly in Figure 9. A pressuregauge 120 is provided for observing thefluid pressure in the gaseousplating chamber.

In order to circulate the gaseous metal compound in contact with themoving sheet or strip 10, suitable baffies 112, 123 are spacedlyarranged longitudinally of the plating. chamber, as illustrated inFigure 9. The gaseous metal compound is admitted through the'conduit116' at one end of the chamber 100 and passes downwardly and upwardlyabout the baffles 112, 123, as, indicated by arrows at 125, the exhaustgases and unused decomposition products are drawn 011 through theconduit 118at the opposite end of the gaseous plating chamber.

The strip 10 after passing through the gaseous metal plating chamber isdrawn outwardly through the exit gate 127 and into the post heatingchamber 102,. and after cooling in the air is stored on the roll 104.

provision of a vacuum or low pressure pre-treatment following theheating of the strip or metal article to be gaseous metal plated.

The vacuum pressures used may vary depending upon the particular metalbeing plated, in each being sutficiently high to produce a perfectly drymetal surface being free of moisture and water vapor and wherein thepores and sub-microscopic depressions-in the metal surface are free ofall occluded gases.

- about the production of a metal product having a metal Guide rolls 78and 79 are arranged in the chamber 65.

and-adapted to support and guide the strip 10 therealong similarlyas-guide rolls 54 and 56 of chamber 47.

.After the metal strip 10 is passed through the gaseous which is ofsimilar construction and operation as gas .10cks40 and.- 60,- and thencethrough the heat treating coating layer which penetrates into the basemetal to provide the same with a layer of metal which is interlockedwith the base metal thus forming a substantially integral metal layertherewith. 5

The invention accordingly provides a method of dry 'platin'g metalarticles' in a manner to provide the same with a coating-metal layerwhich adheres tenaciously to thebase metal forming a coherent,substantially integral .;;body.,. As. is-xwell: known, .inwet'zelectroplating, it has ,been: the practice to applya flash coatingofmetal, such as copper over the base metal to improvethe cohesion ofthe platedmetal. Such practice becomes, entirely un necessary withgaseous metal platinglin accordance with -55 applicants invention.

. In carrying out the gaseousmetal plating in accordance with applicantsprocess, leakage of gas from one compartment to another is efiectivelyprevented by the use of inert gas gatelocks, such as shown at 40,and 60in Figurenlo 2, the inert gas medium used in this instance being carbondioxide, nitrogen or the like, ,the pressure being maintained slightlyhigher than thechamber to be protected so as to cause leakage of theinert vapor into the chamber rather, than leakage of the gas outwardlyof the chambenk:

In this process a stream of gaseous material is conducted into thegaseous platingchamber and'circulated about the heated metal strip. Thegaseous plating atmosphere may be formed by mixingan inert gas with theI vapors of a volatile metal compound or by atomizing aL-='20 liquidmetal compound into a blast of hot inert gas or 1 other equivalentmethod.

Carbon dioxide, helium,.nitrogen, hydrogen, the gaseous product ofcontrolled burning ofhydrocarbon gases free of oxygen, and the like,have been utilized as a car- 2 rier medium or inert gas medium.

In some instances the use of hydrogen is.preferred, as for example, inthe Cleaning anneal chamber where its ability to act as a reducing agentmay be put to advantage to remove the oxide film or rust from iron ormetal strip being plated.

' .iron, chromium, molybdenum, cobalt, and mixed carbonyls. 40

Illustrative compounds of other groups are the nitroxyls, such as coppernitroxyl; nitrosyl carbonyls, for

example, cobalt nitrosyl carbonyl; hydrides, such as antimony hydride,tin hydride; metal alkyls, such. as chromyl chloride; and carbonylhalogens, for example osmium carbonyl bromide, ruthenium carbonylchloride, and the like.

Each material from which armetal may be plated has a temperature atwhich decomposition is complete. However, decomposition may take placeslowly at a lower temperature or while the vapors are being raised intemperature through some particular range. For example, nickel carbonylcompletely decomposes at a temperature in the range of 375 F. to 400 F.However, nickel carbonyl starts to decompose slowly at about 175 F. andtherefore decomposition continues during the time of heating from 200 F.to 380 F.

A large number of the metal carbonyls and hydrides may be eifectivelyand efficiently decomposed at a temperature in the range of 350 F. to450 F. When working with most metal carbonyls we prefer to operate in atemperature in the general decomposition range of the volatilecompounds.

- If the metal is,for example, hot drawn strip, the hot stripuponcooling to the plating temperature range after deaeration may be leddirectly to plating chamber with or without an annealing stagetherebetween. If an anneal is desired, the operation within theapparatus may be carried out in amanner similar to that used whenstarting with cold metal. The metal strip may be raised to and 70maintained at desired temperatures by causing the metal to conductelectricity or by induction heating.

The temperatures in preheating and post heating cham- .;-bersare;considerably;;higherthan plating temperatures,

i.e., in the range of 4 0Q-jF.,-to 1200" F.

'solutely dry metal surface.

. 1 Preparatory to coating the -;strip qtheztmetallic material may becleaned by employingconventional methods used in. the art, comprisingelectro-chemicallyzcleaning by moving the same through abath ofalkali-.or:acid= electrolyte wherein the strip is made the cathode oranode.

Pickling of the metal with hydrochloric, sulfuric: or

I nitric acid, or a combination of acids-,mayyalso be made as apart ofthe cleaning process, and the strip thoroughly rinsed-or washed prior-to introduction ,intotheplating apparatus.

However, if the metal strip is in good condition a cleaning anneal maysuffice, in-which event the strip may be heated just prior to-enteringthevacuumtreatmentcham ber. a

In a cleaning anneal any'grease and the like will be burned away bybringing the strip, to red heat.

The invention will be more clearly understood from the followingdescription of.:one -embodiment 'ofithe. ap-

. paratus and its mode of operation. I

By subjecting the ymetal to beplated .to aipre-heatin treatment prior tothe vacuum or low pressure treatment, occluded gases are more readilyremoved and at a lower vacuum pressure. Thisvacuum deaeration treatmentprior to gaseous metal plating constitutes an essential step of theprocessin order to :produce an ab- The presence of hydrogen, oxygen orwater vapor entrapped or occluded in the pores or irregularities overthesurface of the metal is avoided by the present process and athoroughly coherent metal coating produced.

The post heat treatment of the gaseous plated metal may be omitted ifdesired, but is preferred inmost cases to produce a more even texturedand smoother plating film or coating. The post heat treatment also isadvantageous in preventing the entrainment of moisture. To furtherassist in this, it is, preferable to carry out the post heat treatmentinthe presence of inertgas, e.g., helium, argon, nitrogen, carbondioxide or the like, This may also be accomplished by allowing acontrolled amount of gas leakage of waste gas to take place from ,theplating chamber or by circulating a small amount of the rela- Lrvelyspent or inert gases through the post heating cham The post heatingtemperatures employed will varyfor dilferent metal platings and basemetals. treated as aforementioned. Generally the post temperature is thesame or somewhat higher than the pre-plating heattreatment, the latterbeing governed by the temperature required to effect substantiallycomplete removalof gaseous occlusions in the surface depressions of thebase metal under the reduced pressure conditions. The postjheating, ofthe plated product inaddition to degassing the stripmay be controlled toefiect annealing of the strip. U The duration of heating in bothpre-heating chamber and post heating chamber may be suitably varied toprovide for a heat treatment of from ten to twenty minutes as desired.

The following examples are illustrative but not limitative of theinvention.

EXAMPLE I Nickel-coated steel strip A steel strip which is to be coatedandwhich has been chemically cleaned in the conventional manner ispassed through the rinsing bath and air dried byhot air blast. The stripis then moved along through the pre-heating chamber and subjected to atemperature, of:525? F.', the strip being moved along at a uniformrateand such that the plating time allowed is approximatelytwo to'threeminutes. The heated strip then passes directly: into the 4 low pressureor vacuum chamber where it: is subjected to a vacuum of approximately 1mm. Hg after which the strip is passed along and through thegaseousmetal plating chamber. Nickel carbonyl in theform of vapor andadmixed withcarbon dioxide carrier gasis-fed' to the plating chamber.Approximatelyfiye cubic feet ofinickel carhonylrcarhon dioxideqmixturePer, hour.-.is ;fed;.through the plating chamber, the metal carbonylbeing present in the mixture of vapor is nickel carbonyl and carbondioxide in the proportionate amount of about five ozs. of carbonyl percubic foot of carbon dioxide. The temperature in the plating chamber andstrip is approximately 400 F.

For a plating exposure of two and one-half minutes, this provides acoating of nickel of approximately 0.002- inch which interlocked andpenetrated into the micropore surfaces of the metal is provided. Aftergaseous plating the strip is moved from the plating chamber through thepost heating chamber where it is subjected to a temperature ofapproximately 700 F. in the presence of carbon dioxide.

' EXAMPLE II Nickel coated aluminum Aluminum metal strip is substitutedfor steel strip material and processed as in Example I, except that bothpreheating and post heating treatments are carried out at about 500 F.

EXAMPLE III Cobalt coated steel Steel strip in this example is processedas in Example I, utilizing cobalt carbonyl as the heat-decomposablegaseous metal compound.

The cobalt carbonyl is introduced at a rate of approximately one poundof carbonyl (liquid) per minute. Gaseous plating temperature ismaintained at approximately 425 F. and nitrogen gas used as the carrierin place of carbon dioxide.

EXAMPLE IV Antimony coated copper metal Copper sheet is coated withantimony by first preheating copper strip material free of foreignmatter in an atmosphere of helium at 525 F. The heat treated strip isthen passed into a vacuum chamber where the hot metal strip is subjectedto a vacuum pressure of 50 mm.

Hg and in an atmosphere of carbon dioxide. The strip is then immediatelypassed to the gaseous metal plating chamber where it is subjected to agaseous atmosphere of antimony hydride heated to 400 F. to effectdecomposition and plating out of antimony metal onto the copper strip.The post heat treatment is carried out at a temperature of 475 F. toproduce a final coherent antimony coating on the copper metal basestrip, being integrally united with the copper metal.

While the foregoing examples are given to more particularly point outhow the invention may be practiced, it will be understood that theinvention is not to be specifically limited thereby. The essence of theinvention is the provision of a pre-treatment so as to deaerate orde-gas the metal to be gaseous plated so as to provide a perfectly dry,water-vapor and hydrogen free metal surface for receiving the gaseousmetal plating. The process provides a finished product asaforementioned, wherein the plating or metal coat is interlocked withthe base metal so as to form a substantially integral metal product.

In this connection, Figures and 6 illustrate in enlarged section, theessential difference in structure between 'Wet plated metal products andgaseous or dry plated metal products. As illustrated in Figure 5, metalcoating is applied over conventional treated metal as generally indi-:section a gaseous metal coated structure as produced in In thisinstance, asqg accordance with this invention.

shown, the base metal and metal coating 156 are interlocked to provide asubstantially integral structure. The microscopic pores at the surfaceof the metal are freed of gas occlusions and gaseous metal allowed toenter and thus penetrate into the body of the base metaLdeposition ofmetal taking place to thus provide an interlocking of the metal coatingor. plating with the base metal. I

The foregoing description of a method of gaseous metal plating andproduct obtained thereby is accordingly distinguished from conventionalwet plated products and methods. Whereas the method and apparatusdisclosed herein are susceptible to various changes and modificationswithout departing from the principle and spirit of this invention, it isintended that such modifications as are required to adapt the inventionto different conditions and uses are contemplated as within the scope ofthe invention except as restricted in the appended claim.

What is claimed is:

In apparatus for gas plating metal strip of long continuous length,means comprising cooperating rolls for supporting and moving a metalstrip lengthwise, a plurality of chambers arranged in tandem and throughwhich said metal strip to be gas plated with metal is moved, saidchambers comprising a heating chamber having an inlet and outlet openingfor the passage of said metal strip lengthwise therethrough, means forheating said chamber comprising elongated heating coils arranged invertically spaced relationship and between which said metal strip ismoved, a deaerating chamber connected to the outlet of said heatingchamber, said deaerating chamber consisting of an elongated cylindricalenclosure which is fitted to and arranged to receive said metal strip asthe same moves from the heating chamber, said deaerating chamber havinginlet and outlet openings for passage of said metal strip, meanscomprising a vacuum pump connected to said deaerating chamber forevacuating the same, inert gaseous interlocks disposed at opposite endsof said deaerating chamber to provide a gaseous seal for the deaeratingchamber from the surrounding atmosphere, a gas plating chamber directlyconnected to the outlet of said deaerating chamber and adapted toreceive the metal strip after passing through the deaerating chamber andconvey it along centrally through said plating chamber, inlet and outletopenings in said gas plating chamber, means for introducing aheat-decomposable gaseous metal compound consisting of gaseous nickelcarbonyl admixed with carbon dioxide carrier gas into said platingchamber and discharging the waste products therefrom, said platingchamber including helical-shaped bafile means spacedly arrangedlengthwise of said plating chamber for distributing said gaseous metalcompound evenly in said plating chamber, and means comprising a heatingand annealing chamber directly connected to said gaseous metal platingchamber and arranged to receive the resultant gas plated metal strip asthe same passes therefrom to provide a finished gas plated metal strip.

References Cited in the file of this patent UNITED STATES PATENTS1,497,417 Weber June 10, 1924 1,987,577 Moers Jan. 8, 1935 2,382,432McManus et al. Aug. .14, 1945 2,516,058 Lander July 18, 1950 2,576,289Fink Nov. 27, 1951 2,656,283 Fink et al. Oct. 20, 1953 2,656,284 ToulminOct. 20, 1953 2,685,535 Nack Aug. 3, 1954 2,793,609 Shen et al. May 28,1957 FOREIGN PATENTS 589,966 Great Britain July 4, 1947 OTHER REFERENCESSteel, Gas Plating Offers Versatility, vol. ,113, No. 16, October 19,1953, pages 120, 121 and 124..

